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"To have this happen over the holidays makes it seem all the more unfair," DynCorp CEO says

Monday's incident is the first insider attack involving a female suspect

A Pentagon report says there has been an overall increase in "insider attacks"

An Afghan police officer fatally shot an American contractor at Kabul police headquarters early on Monday, authorities said.

The killing occurred a day after five policemen were killed by their commander in Jawzjan province, in the north.

The incidents added to a number of insider attacks by Afghan soldiers and police officers -- or attackers dressed like them. More than 50 people have been killed in Afghanistan in similar attacks this year, which the Afghan government calls acts of terrorism.

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Sediq Seddiqi, a spokesman for Afghan Interior Ministry, said the woman, around 40, has been a member of the police force for two years. She was arrested and was questioned, he said.

The victim was identified as Joseph Griffin, 49, of Mansfield, Georgia, according to DynCorp International, which describes itself as "a global government services provider in support of U.S. national security and foreign policy objectives, delivering support solutions for defense, diplomacy, and international development."

The civilian contractor for the security assistance force was working as an adviser to Afghan police, said Maj. Martyn Crighton, another ISAF spokesman.DynCorp said Griffin had been supporting the Afghan Ministry of Interior and Afghan National Police Development Program.

Griffin, a veteran of the U.S. military who had served in American-based law enforcement positions, had supported several of the company's global training and mentoring programs since November 2000. He began his most recent assignment in July 2011, DynCorp said.

"Joe spent his career helping people all over the world, most recently working to help the Afghan people secure a better future," said Steve Gaffney, chairman and chief executive of DynCorp International. "The loss of any team member is tragic, but to have this happen over the holidays makes it seem all the more unfair."

A woman who answered the phone at Griffin's home said she had no comment.

"The rise in insider attacks has the potential to adversely affect the coalition's political landscape," according to the report. "It remains clear that the insider threat is both an enemy tactic and has a cultural component," according to the report.

No group immediately claimed responsibility for Monday's attack. But a Taliban spokesman said it carried out Sunday's attack on the five policemen.

In that incident, the police commander who killed the men was a Taliban insurgent who had infiltrated the Afghan police, said Abdul Aziz Ghairat, police chief of Jawzjan province.

The Taliban spokesman said the commander was in touch with the militant group before the attack, and is now in a safe place in their midst.

The Pentagon report said Taliban insurgents have lost some of their punch since their 2010 peak, but they remain "resilient and determined" and "will likely attempt to regain lost ground and influence" through assassinations, high-profile attacks, the use of roadside bombs and other violence.

Also Monday, an ISAF service member was killed in an insurgent attack in eastern Afghanistan.

Per policy, ISAF did not release the service member's name or nationality.